Configuration responsive descent rate warning system for aircraft

ABSTRACT

Warning systems that monitor the altitude above ground and descent rate of an aircraft and generate a warning if the descent rate of the aircraft is excessive for the altitude in which the aircraft is flying are well suited to aircraft whose flight and operational characteristics are readily predictable but not as suitable for aircraft, such as tactical aircraft whose operating conditions are not so predictable. To overcome this problem, the criteria for providing the warnings are altered (30, 32) as a function of flight configuration (16, 18) to optimize the warnings for different flight conditions.

This application is a continuation of application Ser. No. 06/704,364,filed Feb. 22, 1985, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to ground proximity warning systemsand, more particularly, to a system that provides a warning to the pilotof an aircraft if the descent rate of the aircraft is excessive for thealtitude at which the aircraft is flying. The criteria for determiningwhether or not such a warning is to be generated are alterable as afunction of the configuration of the aircraft. Such a warning system isparticularly useful for carrier based anti-submarine aircraft such asthe Lockheed S3-A.

2. Description of the Prior Art

Systems for providing the pilot of an aircraft with a warning in theevent that the aircraft is descending too rapidly are known. Examples ofsuch systems are disclosed in U.S. Pat. Nos. 3,946,358; 3,947,808;3,958,219 and 4,215,334, all assigned to the same assignee as theassignee of the present invention.

While all of the above systems serve the basic function of alerting thepilot if the descent rate of the aircraft exceeds a predetermined safedescent rate determined by the altitude above ground of the aircraft,the above systems are designed to operate with transport aircraft whoseoperational and flight conditions are such that the approach and landingconditions are readily predictable. However, for aircraft such as, forexample, military and tactical aircraft whose operational and flightconditions can vary widely, systems designed for aircraft havingpredictable flight parameters tend to provide false or nuisance warningswhere no unsafe condition actually exists, and may provide less than thedesired warning times under other conditions.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide aground proximity warning system that overcomes many of the disadvantagesof the prior art warning systems.

It is another object of the present invention to provide a warning tothe pilot of an aircraft if the descent rate of the aircraft isexcessive for the altitude above ground and flight configuration of theaircraft.

It is yet another object of the present invention to provide a groundproximity warning system for alerting the pilot of an aircraft if itsdescent rate is dangerously high, and where the criteria for determiningwhether the descent rate is excessively high are altered as a functionof flight configuration of the aircraft.

It is another object of the present invention to provide a warningsystem that generates a warning if the descent rate of the aircraft isexcessively high for the altitude at which the aircraft is flying, butdoes not generate an appreciable number of false or nuisance warningswhen used in a manueverable aircraft.

It is yet another object of the present invention to provide a groundproximity warning system particularly useful for tactical aircraftwherein the criteria used to determine whether a warning should begenerated are adjusted depending on the flight configuration of theaircraft.

Briefly, in accordance with a preferred embodiment of the invention,there is provided a system that monitors the altitude above ground andthe descent rate of an aircraft and issues a first aural warning if thedescent rate exceeds a predetermined safe limit for the radio altitudeat which the aircraft is flying. If the descent rate exceeds thepredetermined safe limit by a predetermined margin, a second distinctaural warning is generated to warn the pilot of a particularly dangerousflight condition. The criteria for generating the warnings are alteredas a function of the flight configuration of the aircraft, for example,whether the landing gear is up or down and whether the aircraft isflying a tactical or non-tactical segment of a mission to optimize thewarning criteria for the operational conditions of the aircraft.

DESCRIPTION OF THE DRAWING

These and other objects and advantages of the present invention willbecome readily apparent upon consideration of the following detaileddescription and attached drawing wherein:

FIG. 1 is a logical block diagram of the warning system according to theinvention;

FIG. 2 is a graph of the descent rate required to generate the twowarnings as a function of radio altitude when the aircraft is operatingin a gear up configuration;

FIG. 3 is a graph of the descent rates required to generate the twowarnings as a function of radio altitude when the aircraft is operatingwith its landing gear down; and

FIG. 4 is a graph of the descent rate required to generate the twowarnings as a function of radio altitude when the aircraft is operatingin a tactical mode and the landing gear is up.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawing with particular attention to FIG. 1, thereis illustrated an embodiment of the configuration responsive groundproximity warning system according to the invention generally designatedby the reference numeral 10. The system 10 according to the invention isillustrated in FIG. 1 in logical block diagram form as a series ofgates, comparators and the like for purposes of illustration; however,it should be understood actual implementation of the logic can be otherthan as shown in FIG. 1, with various digital and analog implementationsbeing possible. The signals used by the system as described includeradio altitude and barometric altitude rate, a signal indicative of atactical mission, for example, a mission selector switch, a landing gearposition switch, a weight on wheels switch and various validity signals.Depending on the type of aircraft on which the warning system isinstalled, the signals shown in FIG. 1 can be obtained from individualinstruments such as an air data computer 12, a radio altimeter 14, agear position switch 16, a mission selector switch 18 and a weight onwheels switch 20. Alternatively, the barometric rate signal may beobtained by differentiating a barometric altitude signal from abarometric altimeter, or the Z-velocity signal from an inertialnavigation system may be used to obtain descent rate information. Also,rather than obtaining the signals from individual instruments, thesignals can be obtained from a digital data bus in certain neweraircraft.

As previously stated, the system according to the invention compares thealtitude above ground with the descent rate, preferably barometricdescent rate or Z-velocity, and issues a warning if the descent rate isexcessive for the altitude at which the aircraft is flying. Thecomparison function is provided by two mode comparators 22 and 24 which,in the present embodiment, compare the radio altitude received from theradio altimeter 14 via a filter 26 which removes high frequencycomponents from the radio altitude signal. The radio altitude signal iscompared with the barometric rate signal that is applied to thecomparators 22 and 24 via a low pass filter 28 and a pair of functiongenerators 30 and 32, respectively. The radio altitude signal is alsocompared with a 2450 foot reference signal and a 30 foot referencesignal by a pair of comparators 34 and 36 to provide enabling signals tothe system when the aircraft is flying between 30 feet and 2450 feet.Although, in the embodiment illustrated in FIG. 1, the comparators andfunction generators have been illustrated as separate components forpurposes of clarity, the comparison function required to generate theappropriate warnings could be provided by a single comparator, orotherwise. For example, the function generation and comparison functionscould be combined in a single block.

In addition to the comparison and warning generation functions discussedabove, the system utilizes a plurality of gates and discrete switches toenable the system only during predetermined phases of flight. Theseenabling functions are provided by the weight on wheels switch whichcooperates with an inverter 38 and a delay circuit 40 to close a switch42 to permit the barometric rate signal to be applied to the filter 28only when there is no weight on the wheels of the aircraft, that is, theaircraft is off the ground. In addition, a series of AND gates 44, 46and 48 and delay circuits 51 and 53 enable the system only when thesignal from the radio altimeter and the air data computer are valid,when there is no weight on the wheels and when the aircraft is flyingwithin a predetermined range of altitudes, for example, between 30 and2450 feet.

In addition, the system includes a pair of aural warning generators suchas a sink rate warning generator 50 and a pull up warning generator 52that are activated by signals received from the gates 46 and 48 via apair of delay circuits 54 and 56 and apply either a "SINK RATE" or a"PULL UP" warning to a transducer 58.

In operation, whenever the aircraft is flying between 30 and 2450 feetthe gates 44, 46 and 48 are enabled and the switch 42 is closed so thatthe barometric rate signal is applied to the function generators 30 and32. Under these conditions, if the combination of descent rate andaltitude above ground is such that the warning criteria established bythe function generator 30 and the comparator 22 are exceeded, the sinkrate comparator 22 will apply a signal to the AND gate 46, therebycausing the AND gate 46 to apply a warning initiation signal to the sinkrate generator 50 after delay circuit 54 has operated. Similarly, if thecombination of descent rate and altitude above ground is such that thewarning criteria established by the function generator 32 and thecomparator 24 are exceeded, the comparator 24 will apply an enablingsignal to the AND gate 48 to apply a warning initiation signal to thepull up warning generator 52, after the delay circuit 56 has operated.The sink rate and pull up warning generators 50 and 52 are preferablydigital voice generators that apply the warnings to the transducer 58either directly or indirectly, for example, through the intercom systemof the aircraft.

As previously stated, the criteria for determining whether a sink rateor a pull up warning are to be generated are determined by theconfiguration of the aircraft. In the illustrated embodiment, themodification of the warning criteria is accomplished by modifying thecharacteristics of the function generators 30 and 32 by discrete signalsfrom the gear position switch 16 and the mission selector switch 18. Themission selector switch is actuated by the pilot whenever a tacticalmission, such as an anti-submarine reconnaissance or attack mission isbeing flown. In the illustrated embodiment, the function generators 30and 32 are altered to modify the barometric rate signal from the filter28 in order to obtain the desired warning criteria; however, inalternative embodiments the radio altitude signal could be alteredinstead.

When the aircraft is flying with its gear up, the function provided bythe function generator 30 is selected such that the "SINK RATE" warningwill be generated whenever the relationship between the descent rate andthe radio altitude is such that it falls within the envelope below theline 100 (FIG. 2). The "PULL UP" warning will be initiated if theenvelope below the line 102 is penetrated. Because of the delaysprovided by the delay 54 (0.8 second) and the delay 56 (1.6 seconds) theactual warning will not occur until the envelope illustrated by thedashed lines 100' and 102' is penetrated. Thus, the delays serve toreduce nuisance warnings in instances where the envelopes 100 and 102are only momentarily penetrated.

Whenever the aircraft lowers its landing gear, and is not in a tacticalmode, the warning criteria are altered as is shown in FIG. 3 to make thewarning system more sensitive at higher altitudes. Thus, with thelanding gear down, the "SINK RATE" warning will be given at a descentrate of 9800 feet per minute at an altitude of 2450 feet as opposed tothe 11,800 feet per minute descent rate required at the same altitudewith the landing gear up. Similarly, the pull up warning will be givenat 12,550 feet per minute at 2450 feet rather than at 14,700 feet perminute. This takes into account the reduced recovery capability of anaircraft when the landing gear is down.

Whenever an aircraft is in a tactical phase of flight, such as, forexample, when it is attacking a target, higher descent rates areencountered than are encountered in a non-tactical phase of flight.Thus, the warning criteria must be modified accordingly, in order toavoid nuisance warnings, and the criteria illustrated in FIG. 4 areutilized to provide additional maneuvering room for the aircraft beforea warning is generated. These criteria are used only when both thelanding gear is up and the mission selector switch indicates a tacticalmode of operation.

The tactical mode criteria require a 13,800 foot per minute and a 16,700foot per minute descent rate before the "SINK RATE" and "PULL UP"warnings, respectively, are generated when the altitude of the aircraftis 2450 feet. In addition, the descent rates required for a warning tobe generated at low altitudes, for example, below 450 feet, are alsosubstantially increased. For example, at 450 feet a 3800 foot per minutedescent rate is required before the "SINK RATE" warning is generated,and at 30 feet of radio altitude, a descent rate of 2960 feet per minuteis required. To generate a "PULL UP" warning at 30 feet of radioaltitude, a 3474 feet per minute descent rate is required, and 3800 feetper minute is required at 300 feet of radio altitude. Thus, the systempermits the aircraft to maneuver at low altitudes, for example, as itdoes during submarine reconnaissance missions without generatingnuisance warnings.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. Thus, it is to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described above.

What is claimed and desired to be secured by Letters Patent of theUnited States is:
 1. A warning system for warning the pilot of anaircraft of an unsafe flight condition comprising:means for receiving asignal representative of the descent rate of the aircraft; means forreceiving a signal representative of the radio altitude of the aircraft;means for receiving a signal representative of the position of thelanding gear; means responsive to the descent rate representative signaland the radio altitude representative signal for generating a firstwarning signal when the descent rate at the altitude at which theaircraft is flying exceeds a first predetermined value which isdetermined for the aircraft when its landing gear is down; meansresponsive to the descent rate representative signal and the radioaltitude representative signal for generating a second warning signalwhen the descent rate at said altitude exceeds a second predeterminedvalue, said second predetermined value being relatively larger than saidfirst predetermined value and determined for the aircraft when itslanding gear is up; means responsive to the landing gear positionrepresentative signal for selecting said first warning generating meansor said second warning generating means as a function of the landinggear position; means for detecting whether the aircraft is in a tacticalmode of operation; means responsive to said descent rate representativesignal for generating a third warning signal when the descent rate atthe altitude at which the aircraft is flying exceeds a thirdpredetermined value being relatively greater than said secondpredetermined value and determined for the aircraft when it is in atactical mode of operation with its landing gear up; and meansresponsive to said detecting means and said landing gear representativesignal for selecting said third warning generator means when theaircraft is in a tactical mode of operation with its landing gear up.